Method for selective extraction of compounds from carbonaceous materials

ABSTRACT

An improved low temperature process for extracting oil from oil-bearing materials by extracting the oil-bearing material in an extraction zone with a normally gaseous solvent selected from propane, butane, and mixtures thereof. As the resulting solvent/oil mixture is passed through the bed of extracted oil-bearing material, from the extraction zone, and to a separation zone, it is done so under conditions that will maintain the solvent in liquid form. The resulting extracted materials have substantially more of their protein and vitamin value intact when compared with similar materials extracted by more conventional high temperature methods. The present process is also a lower energy consuming process than more conventional, extractive processes.

This is a 371 application of PCT/US92/11394 filed Dec. 31, 1992.

FIELD OF THE INVENTION

The present invention relates to methods for selective extraction ofdesired compounds from carbonaceous materials, and more particularly toa solvent extraction process for the removal of selected compounds fromcarbonaceous materials.

BACKGROUND OF THE INVENTION

In many instances the characteristics of a particular carbonaceousmaterial can be altered by the removal of certain compounds from thematerial. Examples of some compounds which it may be desirable to removewould include: phospholipids, fats, fatty acids, alcohols, waxes, gums,stearols, oil soluble proteins, flavonol, mineral oils, essential oils,and PCB's.

More particularly, oils derived from plant materials, such as oil-seeds,cereal brans, fruits, beans, and nuts, are the source of raw materialfor many important commercial products. For example, such oils from suchplant materials are extensively used in cooking, low fat and fat freecooked food, in cosmetics, pharmaceuticals as carriers for insecticidesand fungicides, in lubricants, and in myriad other useful products.Consequently, much work has been done over the years in developingimproved processes for extracting oil from such materials.

One of the most widely used processes for removing oil from oil-bearingmaterials is solvent extraction. In solvent extraction, the oil-bearingmaterial is treated with a suitable solvent, usually the lower carbonalkanes such as hexane, at elevated temperatures and low pressures, toextract the oil from the oil-bearing material. The resulting solvent/oilmixture is then fractionated to separate the valuable oil from thesolvent, which is recycled. Most solvent extraction processes incommercial use today employ hexane as the solvent. While hexaneextraction is the most widely used today, there are also teachings inthe art in which normally gaseous solvents are used at bothsupercritical and subcritical conditions.

One such teaching is found in U.S. Pat. No. 1,802,533 to Reid, wherein anormally gaseous solvent, preferably butane or isobutane, is liquefiedby decreasing the temperature and/or increasing the pressure, thenpassing the solvent through a bed of the oil-bearing material in anextraction vessel. The solvent and extracted oil are then passed to astill where the solvent is separated from the oil. The extractedmaterial must then be placed in another still where it is heated toremove solvent which remained entrained in the extracted material. Thereis no suggestion of obtaining a substantially solvent-free, dry,extracted material without an additional treatment step afterextraction.

Another extraction process is taught in U.S. Pat. No. 2,548,434 toLeaders wherein an oil-bearing material is introduced into the top of anextraction tower and passed counter-current to a liquefied normallygaseous solvent, such as propane, which is introduced at the bottom ofthe extraction tower. The tower is operated near critical conditions sothat the solvent selectively rejects undesired color bodies,phosphatide, gums, etc. The resulting solvent/oil mixture can then beflashed to separate the solvent from the oil. In another embodiment, thesolvent/oil mixture is first subjected to a liquid/liquid separationresulting in one fraction containing solvent and a less saturated fattymaterial, and another fraction containing solvent and a more saturatedfatty material. The solvent is then flashed from both fractions. Theextracted material remaining in the tower is drawn off and subjected toa vacuum flashing operation to remove entrained solvent.

U.S. Pat. No. 4,331,695 to Zosel teaches a process for extracting fatsand oils from oil-bearing animal and vegetable materials. The materialis contacted with a solvent, such as propane, in the liquid phase and ata temperature below the critical temperature of the solvent to extractfat or oil from the material. The resulting solvent/oil mixture istreated to precipitate the extracted fat or oil from the solvent byheating the solvent to above the critical temperature of the solventwithout taking up heat of vaporization. The extracted residue (shreds)is then treated to remove any entrained solvent, either by blowing itdirectly with steam, or by indirect heating followed by direct steaming.

In U.S. Pat. No. 5,041,245 to Benado a continuous solvent extractionmethod utilizing propane is disclosed to remove oils from vegetablematter, particularly rice bran. According to this method a sufficientamount of liquid sealing medium is first injected into the vegetablematter in a feeding zone to form a dough-like plastic mass which iscompacted and transported by a conveyor assembly to an extraction zoneto form a bed. Propane is then introduced into the bed of the extractionzone being operated at 102°-122° F. and 125-250 psi to react with thebed material. The miscella of extracted oil and solvent resulting fromthis from the reaction of propane and bed material is then separatedfrom the remaining solid residue of the bed material. The propane isthen separated from the extracted oil by evaporation or volatizationmethods. The preferred separation method is to first subject themiscella to near its critical pressure (600 psi for propane/rice branoil mixture) and significantly elevated temperatures (190°-200° F. forpropane/rice bran oil mixture) which can also be near critical. Thisyields a high solvent light phase (98% solvent, 2% bran oil) and anoil-enriched heavy phase (60% solvent, 40% bran oil). The oil enrichedheavy phase under reduced pressure is then delivered to aheater-evaporator and further treated to form a more oil-enriched heavyphase (10% solvent, 90% bran oil). This phase is then de-pressurized toabout one atmosphere, and further treated in a second combinedheater-evaporator stage to produce an oil stream having not more than1-2% propane. Further similar treatment of this oil stream could beaccomplished to remove additional propane if desired.

Other references which teach solvent extraction of oil-bearingmaterials, with normally gaseous solvents, include U.S. Pat. Nos.2,682,551 to Miller; and 2,560,935 to Dickinson. In each of theseprocesses, the extracted material must be further processed to removeentrained solvent.

While prior art extraction methods, particularly hexane extraction, havemet with various degrees of commercial success, there still remains aneed in the art for an improved solvent extraction method which is moreenergy and cost efficient, which can effectively remove the solvent fromthe extracted compounds to meet government regulations, which isespecially suitable for the processing of certain troublesomeoil-bearing materials, as well as which allows greater selectivity ofthe compounds removed from the carbonaceous material and which resultsin the recovery of de-oiled products having superior nutrient and healthcharacteristics.

In solvent extraction of oil from carbonaceous materials, such asvegetable material, one problem has been fluidization problems in thebed formed by the material in the extraction vessel. This has lead tothe need to pre-pelletize or compact the material before placing thematerial in the extraction vessel to increase the material bedpermeability and allow the solvent to penetrate and flow through allportions of the material bed. This problem is particularly acute inthose situations where a significant amount of the vegetable materialare of small particle size, e.g., 100 to 400 mesh.

When the carbonaceous material contains significant amounts of oil,current solvent extraction methods have been inefficient for removingmost or all of the oil. Examples of such material would include jojoba,cocoa, rape seed, and canola which are 30%-60% by weight oil. In theseinstances it has been necessary to first press the material to remove amajority of the oil before using solvent extraction methods to removethe remaining amounts of oil. Alternatively, the material could be firstmechanically ground or pulverized to render the oil more accessible toreaction with the solvent. This latter method is difficult if thematerial has a high oil content.

In many of the instances where the material must first be pressed it isnecessary to subject the material to high temperatures (200°-360° F.) toeffectively remove the oil. In food material such high temperatures canresult in deleterious effects to the desirable characteristics of thematerial, such as protein denaturing, vitamin destruction, and creationof carbonic acids which effect the aromatic odor of food material suchas spices and herbs.

One particularly troublesome material is rice bran, one of the mostplentiful and nutritious food sources known to man, but which is greatlyunder utilized. This is primarily because immediately following themilling step, a lipolytic enzyme in the bran is activated whichcatalyzes the hydrolysis of the glyceryl esters of the free fatty acids(FFA) present in the lipids. This is measured by FFA increase, which israpid at typical atmospheric storage conditions. This starts fatty acidformation and bran rancidity in a matter of minutes after milling, andeventually renders it inedible to humans after several days of storage.Consequently, rice bran, as a source of oil and food, is under utilized,particularly in less developed countries. While the food industrystruggles to find ways to obtain a rice bran, and rice bran oil, free ofthese undesirable characteristics, more and more beneficial uses andnutritive values are being discovered for these products. For example,it has recently been reported that rice bran fiber is effective forlowering cholesterol in humans. As a result, a tremendous demand hasbeen created for a process which can stabilize the rice bran aftermilling, or a process which will allow for the extraction of oil whileat the same time stabilizing the oil and bran against further fatty acidformation.

Other problems are encountered with different food products. Forexample, in eggs it is desirable to remove the cholesterol from theyoke, yet have the eggs retain their natural proteins not denatured,texture, and taste when cooked. This has not been possible with thepresent known methods of solvent extraction.

As another example, in many commercially available seasonings and foodcoating products one problem has been the inability to remove certainfats while retaining the flavoring of the products.

Still another problem has been to create seasoned or unseasoned foodcoatings that have dielectric characteristics which increase the abilityof the coating to adhere to the food product during handling andcooking. A further problem with food coatings occurs when the foodproduct is mircowaved. The moisture in the food product permeates thecoating during the cooking process resulting in a soggy,unappetizing-looking crust.

Still other problems occur when trying to remove oils and fats fromfried products such as potato chips and french fries. Current methodsresult in undesirable flavor or texture changes because of the inabilityof these methods to selectively remove only the undesired compounds.

The treatment of animal products by present solvent extraction processesto remove fats and cholesterol have not been commercially successfulbecause of the dilatory effect on the taste, color or texturecharacteristics of the cooked animal products.

SUMMARY OF THE INVENTION

Therefore one object of this invention is to provide a solventextraction process for selectively extracting substances fromcarbonaceous materials.

Another object of this invention is to provide a solvent process for theselective removal of various oils from food products that allows forcost effective removal of the solvent from the extracted oils andde-oiled products which meet current governmental regulations for lowfat and fat free claims.

Still another object of this invention is to provide a solvent processfor the selective removal of undesirable substances from food productswhich does not destroy the flavor, texture and/or color characteristicsof the food product.

A further object of this invention is to provide a solvent process forthe selective removal of undesirable substances from food coatings whichalso increases their dielectric characteristics.

A still further object of this invention is to provide a solvent processfor the selective removal of undesirable substances from food coatingswhich also effects better sealing of moisture in the food product duringcooking resulting in crisper, more appetizing products.

Another object of this invention is to provide novel oils and othersubstances having more desirable food consumption characteristics.

Another object of this invention is to provide a novel rice bran oil andde-oiled rice bran.

A further object of this invention is to provide a novel meat product.

A still further object of this invention is to provide a novel foodcoating product.

Other objects and advantages of this invention will become apparent fromthe ensuing descriptions of the invention.

Accordingly, a method for removal of selected substances fromcarbonaceous material by use of a solvent is provided comprising: (a)introducing the carbonaceous material containing the selected substancesinto an extraction zone to form a bed; (b) introducing a gas which at agiven temperature liquifies at a higher pressure than the solvent, theintroduction being made under a pressure and at a temperature to causethe temperature and pressure of the extraction zone to be sufficient tocause the solvent to liquify when the solvent is introduced to theextraction zone; (c) introducing into the extraction zone the solventcapable of extracting the selected substance; (d) passing the solventthrough the bed of carbonaceous material to extract the substances fromthe material; (e) removing the resulting substance/solvent mixture fromthe extraction zone to a separation zone under conditions which willmaintain the solvent in liquid form as it is passed through the bed ofcarbonaceous material and out of the extraction zone to the separationzone; and (f) separating the solvent from the substances in theseparation zone.

In a preferred embodiment of the present invention, thesubstance/solvent mixture is removed by introducing a second compound,such as nitrogen, methane, or CO₂, having dissimilar and greatervaporization conditions from the solvent which is used to not only purgethe extracted compound/solvent mixture from the extraction zone, but tomaintain the temperature and pressure so that the first introducedsolvent is maintained in liquid form during the purging and movement tothe separation zone.

In another preferred embodiment of the present invention, the materialin the extraction zone is stressed by increasing for short periods oftime pressure differential between the top and bottom of the extractionzone bed.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a simplified schematic drawing of a preferred solventextraction process of the present invention.

FIG. 2 is a schematic representation of the reaction vessel utilized inexperiments described below.

FIG. 3 is a graphical representation of the results of tests runutilizing the process of this invention in extracting oils from ricebran.

FIG. 4 is a graphical representation of the results of tests runutilizing the process of this invention in extracting oils from certaincommercially available cooked food products primarily fried foodproducts.

FIG. 5 is a graphical representation of the results of tests runutilizing the process of this invention indicating the effect on theflavor, color and shape of certain commercially available cooked foodproducts.

FIG. 6 is a graphical representation of the results of tests runutilizing the process of this invention in extracting butter fat fromcertain name brand cocoa powders.

FIG. 7 is a tabular representation of the characteristics of a rice brande-oiled in accordance with the process of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Any carbonaceous material can be treated to selectively removesubstances by the solvent extraction method of the present invention.Non-limiting examples of such carbonaceous include soybeans, cottonseed,linseed, and cereals such as rice bran, wheat bran, and corn meal, aswell as small particle products such as food coatings, meats.Non-limiting examples of the types of substances which can be removedfrom such materials include phospholipids, fats, fatty acids, alcohols,waxes, gums, stearols, oil soluble proteins, flavonol, mineral oils,essential oils, oils from cooked or processed food, and PCB's.

Solvents suitable for use in the present invention are any solvent whichis normally a liquid at extraction conditions, and in which thesubstance to be extracted is soluble under the reaction conditions. Theselection of the appropriate solvent (or combinations of solvents) canthus be made based on its (their) known solubility characteristics. Ifthere is to be selective removal of substances, then the solubility ofthose substances must be considered in the selection of the solvent (orcombination of solvents), as well as the operating conditions used inthe process. In certain circumstances, such as when treating foodproducts, other known characteristics of the solvent may need to betaken into account.

Without limiting the scope of this invention, the preferred embodimentsare described as applied to the treatment of certain food products toremove oils, waxes, gums, fats, and/or cholesterol.

Depending on the particular type substances being removed solventssuitable for use in the present invention would include any solventwhich is normally a liquid at extraction conditions, such as hexane, orwhich can be converted to a liquid at extraction conditions. Preferredsolvents are those which are normally gaseous at typical atmosphericconditions. That is, those which are a gas at about room temperature(about 70° F.) and atmospheric pressure. Non-limiting examples ofpreferred solvents include methane, ethane, propane, butane, ethylene,propylene, butylene, sulfur dioxide, carbon dioxide, CHF₃, CClF₃, CFBr₃,CF₂ ═CH₂, CF₃ --CF₂ --CF₃, CF₄, CF₄, CH₃ --CF₃, CHCl₂, ammonia,nitrogen, dichlorodifluor methane, dimethylether, dimethylsufaoxide(DMSO), acetone, nitrious oxide, methyl fluoride, and halogenatedhydrocarbons or combinations thereof which are normally gaseous asindicated, as well as various alcohols. For removal of oil from ricebran and similar grains preferred solvents are propane, butane, andmixtures thereof; and, more preferred is propane.

The weight ratio of solvent to oil-bearing material will be from about1:1 to 2:1, preferably from about 1.2:1 to 1.5:1. A cosolvent, such as aC₂ to C₆ alcohol, preferably ethanol, may be used. If a co-solvent isused it may be used in place of at least about 0.5 to 90 vol. %,preferably about 5 to 50 vol. %, and more preferably from about 5 to 25vol. %, of the primary solvent.

Referring now to the Figures, oil-bearing material is introduced intoextraction zone E via line 10. The extraction zone can be comprised ofone or more vessels suitable for the volumes, temperatures, andpressures employed. For illustration purposes, only one vessel is shown,but in actual practice it would be preferred to use two or more vessels.In this way, while a vessel has undergone extraction and is beingunloaded, another vessel can be loaded with the oil-bearing material tocontinue the extraction process. This would represent a continuous typeof operation. Unlimiting types of vessels which may be used in theextraction zone include fixed-bed, slurry-bed, moving-bed, as well asreactors in which the oil-bearing material is fed therethrough on or ina bucket, a belt with perforations, or with a screw. It is preferredthat the vessel be one in which a limited fixed-bed of oil-bearingmaterial can be loaded with a sealing piston. It is preferred toevacuate the vessels of the extraction zone prior to the introduction ofsolvent, especially if the solvent is propane which may form anexplosive mixture with air. The evacuation can be conducted in anysuitable manner, such as, by use of a vacuum pump or by merely ventingthe air as it is displaced by the solvent during solvent loading orcirculating N₂ or CO₂ through the bottom and out the top. Becausecertain solvents, such as propane, can become explosive when mixed withair special conditions or steps may be needed if such a solvent isselected. Such conditions or steps are well known in the art. Of courseany propane which contaminates the vented air can be separated bypressure or membranes, etc. or burned-off as a heat source duringventing.

It is also within the scope of the present invention that the extractionzone be flushed with inert gas prior to introduction of the solvent.That is, by displacing the air in the extraction zone with the inertgas. It is preferred that the inert gas be at elevated temperatures, forexample at a temperature from about 80° to 400° F., but which does notheat the material beyond 140° F., preferably from about 55° to 120° F.,during the heat transfer. This hot inert gas flush will act asevacuating the extraction zone of air as well as heating, or drying, theoil-bearing material.

It is preferred that the oil-bearing material be dry before beingcontacted with the solvent to mitigate any freezing which may occurduring the process. While the hot inert gas can be used to dry theoil-bearing material, it may also be dried by any other appropriatemeans, such as by heating it by conventional means, including the use ofmicrowaves. Furthermore, after flushing the extraction zone with inertgas, the inert gas can be used to pressurize the extraction zone so thatwhen the normally gaseous solvent is introduced into the extraction zoneit is immediately transformed to the liquid state to preventrefrigeration freezing.

Returning to the Figures, the normally gaseous solvent is fed into theextraction zone via line 12 in the vapor state, under an effectivepressure and temperature which will cause the normally gaseous solventto liquefy. It is also within the scope of this invention that thenormally gaseous solvent be introduced into the extraction zone alreadyin a liquid state. The inert gas can also be used to pressurize theextraction zone so that as the normally gaseous solvent enters theextraction zone, it is converted to its liquid form. Typically, theextraction temperature will be from about ambient temperature, up to,but not including, the temperature at which degradation, or denaturing,of the proteins of the oil-bearing material is initiated. It is alsodesirable to protect the vitamins against degradation. This temperaturewill typically range from about ambient temperature to about 140° F,preferably from about 60° F. to 130° F., more preferably from about 70°F. to 120° F., most preferably from about 70° F about 110° F. For heatsensitive material such as dried egg yolks it is preferred that thetemperature be 60°-90° F. It is within the scope of this invention tooperate the extraction zone at a temperature and/or pressure which willselectively remove the oils, but leave any substances such as gums andwaxes in the extracted oil-bearing material, or to selectively extractthe phospholipid gums and waxes with the heavier oil fractions. Such atemperature will typically be less than about 80° F. at aboutatmospheric pressure. Of course, the temperature may vary somewhat atdifferent pressures. In addition, these temperatures may vary for anygiven oil-bearing material and solvent combination, and the preciseconditions are within the skill of those in the art given the teachingherein. After the oil has been removed, it is then possible to similarlytreat the remaining material, but at slightly elevated temperaturesand/or pressures conditions to remove the waxes and gums. The abovestated conditions are the preferred conditions when the oil-bearingmaterial is rice bran and the solvent is propane. Since the de-oiledrice bran is a commercially important product it is preferred that thetemperature not be so high that the proteins and vitamins of the ricebran are destroyed during the extraction process. The pressuremaintained in the extraction zone will be a pressure which is effectivefor maintaining the solvent as a liquid, and to drive the oil/solventmixture rapidly through the vessel. While this pressure will bedependent on such things as the particular solvent and temperatureemployed, for propane it will typically range from less than atmosphericpressures to about 250 psig, preferably from about -15" Hg to 200 psig,more preferably from about 100 psig to 140 psig.

The extraction zone can also be subjected to conditions which willrepeatedly stress and relax the oil-bearing material and/or solventmolecules. This is believed to create a washing effect that enhances theability of the solvent to extract the oil from the material. In additionit is believed that such pressure pulsing aids in the separation of theheavier oil from the lighter solvent after the oil has been extractedfrom the material and while it is flowing toward the bottom of thereactor. Such stressing and relaxation are effected to create pressuredifferentials between the top and bottom of the extraction zone of atleast 0.25 psig. The pressure differential can be as great as willpermit, under the temperature and pressure conditions of the materialbed, the solvent passing through the exit port of the reactor to remainas a liquid.

This pressure differential can also be created by actuating anddeactuating a piston or diaphragm in the pressure or solvent line. Thestressing and relaxation conditions can also be caused by sonification;i.e., by subjecting the ingredients of the extraction zone to sonicenergy.

In a particularly preferred method a second solvent or inert gas isintroduced to the top surface of the extraction zone to increase thepressure and then briefly open a valve in the separation zone to causethe second solvent or inert gas to displace part of the propane/oilmixture through the bottom filter. In this manner it acts as a fluidpiston. This action allows the bed to be comprised of much smallerparticles than has generally heretofore be used in solvent extractionprocesses. There is no need to pre-pelletize such particles beforetreatment.

This also allows the utilization of the forces of polarity incombination to extract different materials at the same time by usingpressure from the second gas. By selecting a second solvent having adifferent polarity that solvent can be used to remove differentsubstances, such as cholesterol from egg powders.

The period of time that the valve remains open would be sufficient topermit at least some of the extracted oil and propane to flow throughthe bottom filter in the reaction vessel and into the separation zone.The extracted oil and propane can at that time be separated if desired.After the valve is closed additional liquid propane or N₂ is then addedto the bottom of the extraction zone to again raise the pressure andclear the filter in the extraction zone and purge the second solvent orinert gas. If another compound was extracted by the second solvent, thenthe mixture of the second solvent and this other compound will be forcedthrough the top filter of the extraction zone and into an upperseparation zone where the other compound can be recovered by knownseparation techniques.

In an alternate embodiment the bottom valve can be continuous open, andthe top valve of the reactor through which the second gas enters theextraction bed can periodically be opened. This is achieved by settingthe pressure at the top valve sufficient higher than the desiredpressure in the extraction bed, and by opening the top valve before thepressure at the bottom valve reaches a pressure too low to maintain theextraction bed pressure at the desired level.

The pulsing procedure may be repeated as many times as desired and withthe proper construction of the reaction vessel utilizing many differentsolvents. The number of pulsings, as well as the amount of the pressuredifferential, and the time between pulses, depends on the accessibilityof the oil in the oil bearing material for contact by the solvent, aswell as the polarity strengths of the substances involved; i.e., howstrongly bonded the oil is to other substances, such as the proteins, inthe product.

The extraction can also be accomplished in more than one extractions;i.e., the oil-bearing material can undergo several extractions withfresh solvent in order to assure more complete removal of oil. Forexample, a first extraction may leave as much as about 1 to 3 vol. % ofthe oil in the material which weight percent is based on the totalweight of the extracted material. A substantial amount of this residualoil can then be removed by subjecting the oil-bearing material to atleast one other extraction with fresh solvent. It is preferred that lessthan about 1 wt. %, more preferably less than about 0.1 wt. % of theextracted material represent that residual oil fraction in the de-oiledmaterial. Of course, the economics of the process must be considered sothat the cost of additional extractions does not exceed the value of theadded products from the additional extractions.

The oil-bearing material preferably sits on a filtering means, such as ascreen, or membrane filter, or perforated tray (not shown), wherein thesolvent passes there-through with the extracted oil. It is understoodthat an alternative process feature is one wherein the filtering meansis situated between the extraction zone and the separation zone. Thesolvent is maintained in contact with the oil-bearing material for aneffective period of time. That is, for a period of time which willresult in the extraction of a predetermined amount of oil. Of course, iftoo much oil still remains in the oil-bearing material after extraction,it may be subjected to one or more additional extraction cycles or theextraction time extended with pressure pulsing according to thecondition of the oil-bearing material feedstock or the desired productto be recovered.

The solvent/oil mixture is passed from the extraction zone via line 18to separation zone S under conditions which will maintain the solvent asa liquid. It is important that the pressure be maintained in theextraction zone during removal of the solvent and oil not only toprevent unnecessary evaporation of solvent during removal which mayresult in freezing of the extracted material, but also to not complicatethe removal of excess solvent in the material to less than thatpermitted by government regulations. A preferred method of maintainingthe pressure in the extraction zone during removal of solvent and oil isto introduce a gas which has dissimilar vaporization conditioncharacteristics from the solvent, more particularly vaporizationcondition characteristics greater than the solvent so that it can beused to add pressure and heat to the extraction zone during the removalof the oil/solvent mixture to prevent freezing of the oil bearingmaterial, the remaining oil/solvent mixture, and the extracted mixture.

Such gases would include an inert gas, such as nitrogen, into theextraction zone to replace the leaving solvent/oil mixture. By "inertgas" is meant a gas which will not cause a deleterious reaction of theextracted oil or extracted material. The preferred inert gas isnitrogen, carbon dioxide or methane. More preferred is nitrogen. The gasreplaces the solvent/oil mixture in the extraction zone and maintainssubstantially the same pressure throughout the solvent/oil removal step.This prevents freezing of the extracted material. It is preferred thatthe inert gas which is introduced into the extraction zone to displacethe solvent/oil mixture be heated. That is, that it be at a temperaturefrom about 60° F. to 140° F., preferably at a temperature from about100° F. to 120° F. This heated inert gas can enhance the recovery of anyresidual oil and solvent left in the extracted material.

It is also preferred that in designing the reactor vessel and inselecting the solvents to be used, the specific gravities of thesubstances to be removed and the specific gravity of the solvents be asdifferent as possible. This has found to be beneficial in the separationof the oil and solvent from each other, as well as the oil bearingmaterial, during the pulsing stages. For example the large differentialin the weight of propane and oil causes the propane to separate from theoil and move upward in a purified form to contact more oil still boundin the rice bran while the extracted oil rapidly moves toward theseparation zone for removal. This reduces the amount of solvent neededto remove the oil and/or reduces the amount of separation of solventfrom the extracted oil.

It is also within the scope of this invention that solvent vapor bepassed through the de-oiled material either in place of the inert gas orfollowing the passage of inert gas. This solvent vapor will act toremove at least a portion of the residual oil/solvent mixture left inthe de-oiled material.

The separation zone is run under conditions which will enhance theseparation of solvent from the oil. It is preferred that some heat beapplied preferably from a slightly heated solvent or inert gas, toenhance this separation. Other methods which can be employed foroperating the separation zone to enhance solvent/oil separation includedistillation, centrifugation, the use of membranes and reducedpressures, and/or cryogenics. The separated solvent is then passed, vialine 20, to storage zone ST where it can be recycled via line 22 to theextraction zone. Makeup solvent, if needed, can be added via line 24. Atleast a portion of the recovered solvent may also be recycled directlyto the extraction zone via line 26.

It is also within the scope of the present invention that the separationbe conducted in more than one vessel. For example, the solvent/oilmixture (which may also include some of the second dissimilar gas) mayfirst be subjected to a first separator vessel wherein a liquid/liquid(and gas if the second dissimilar gas is present) separation occurs.That is, the separation vessel is under enough pressure so that thesolvent will not vaporize. The liquid solvent is separated from the oilphase. The liquid solvent fraction is then introduced into a secondseparation vessel wherein a liquid/vapor separation occurs. That is, thesolvent is vaporized and collected in a storage vessel and any residualoil fraction is separately collected. This second vessel will typicallybe smaller than the first and may include the use of a vacuum or otherconventional means to aid in the vaporization of the solvent.

If gums and waxes, or certain oils, are present in the extracted oilfraction, they may be solidified out of the oil by cooling. The coolingcan be provided by use of the vaporized solvent which will still be coolowing to the vaporization step.

The substantially solvent-free oil is collected via line 30. Thede-oiled oil-bearing material can be collected from the extraction zoneby any appropriate means. For purposes of simplification, the de-oiledmaterial is shown in the Figure as being collected via line 32.

In those situations where the oil-bearing material is one which isunstable because of the production of fatty acids, such as rice bran, astabilizing agent can be added to the extraction zone via line 34. Anyappropriate means can be used to add the stabilizing agent. That is, itcan be sprayed directly onto the oil-bearing material prior to thematerial being introduced into the extraction zone. It can also beintroduced into the extraction zone either directly, (as shown in thefigure) or in combination with the solvent. Rice bran, the preferredoil-bearing material, upon milling, activates lipolytic enzymes whichcatalyze the production of free fatty acids. These free fatty acidscause the bran to become rancid. Non-limiting examples of stabilizerswhich can be used to stabilize rice bran include an inert gas such asnitrogen, food grade acids and alcohols, preferably ethanol, mercaptans,and enzyme inhibitors, protein, and/or peptides. Preferred are foodgrade acids and alcohols, non-limiting examples of which include citricacid, ascorbic acid, lactic acid, gluconic acid, malic acid, ethanol andthe like. More preferred are citric acid and ascorbic acid, withascorbic acid being most preferred.

The rice bran which results from the preferred embodiment of the presentinvention is unique in the industry in commercial quantities. That is,not only are the fatty acids stabilized, but deleterious ingredientswhich contribute to poor taste are also absent. Furthermore, the ricebran of the present invention also contains more vitamin B's and evenprotects the cyanocobalamin (vitamin B-12) than an identical bran whichhas been extracted by use of a conventional hexane extraction process.Consequently, the rice bran produced in accordance with the presentinvention fills a long felt need in the art.

Utilizing the reactor vessel 100 schematically illustrated in FIG. 2 theexperiments results of which are described in FIGS. 3-7 were conductedas follows. The rice bran or other material was introduced to theextraction zone 101 of the reactor 100 via line 102. Valve 103operatively attached to line 102 was closed. Nitrogen was thenintroduced into the bottom of extraction zone 101 via line 104 insufficient quantity to purge the air from extraction zone 101 into upperseparation zone 105. The air was then purged from upper separation zone105 through line 106 into the atmosphere. The pressure in extractionzone 101 was then adjusted and maintained at 90 psi. Propane was thenintroduced through line 104 into extraction zone 101 in quantitiessufficient to purge the nitrogen from the reactor 100 through line 106and to increase the pressure within extraction zone 101 to 127 psi.

Nitrogen was then reintroduced through line 107 in quantities sufficientto create a pressure differential between the top and bottom ofextraction zone 101 of 1-50 psi. Valve 106 was then cracked open untilthe pressure differential was dissipated at which time valve 106 wasclosed. This procedure was repeated for about ten minutes byre-introducing nitrogen through line 107.

Nitrogen was then used to purge extracted oil/propane mixture from theextraction zone 101 and from reactor 100 through line 109. At all timesduring the procedure to this phase, the pressure and temperature wasmaintained at levels to prevent the propane from vaporizing while theoil/propane mixture was forced through the 400 mesh bottom filter 108.

Vacuum to 15" Hg is completed and nitrogen at 80° F. was then circulatedthrough the extraction zone 101 to remove all trace amounts of propanewhich remained in the de-oiled rice bran which was removed from reactor100 through line 106.

Upper 200 mesh filter 110 is removed and the de-oiled rice bran wasremoved from reactor 100. The extracted N₂ /oil/propane mixture removedfrom reactor 100 were separated by alternately cooling and heating, anduse of pressure in a separate vessel not shown by well known means.

The de-oiled rice bran or other material was then analyzed. The resultsare summarized below and depicted in FIGS. 3 through 7.

FIG. 3

With regard to the results shown in FIG. 3, the product tested wasstabilized and unstabilized full fat rice bran (not pelletized). The oilvariance ranged from 12% to 18.3% by weight, depending on the hull andrice polish contaminants, with an average of 17.5% by weight. Theresults varied as pressures were increased from 120 psi to 250 psi. Itshould be noted that similar results were found for dry egg yolk,defatted cocoa powder, jojoba bean and soya, although these results werenot directly proportional. For each of the three tests whose results areshown in FIG. 3, the first bar represents oil percentage removed whenthe vapor liquid pressure was not controlled. Due to freezing, limitedheat was applied, and the time was extended four hours for testcompletion.

The second bar represents oil percentage removed when the isothermalvapor liquid pressure was controlled using pulsed nitrogen gas toincrease and decrease the pressure, thus creating a washing action. Thistesting was completed within 45 minutes.

The third bar represents oil percentage removed when the gums, waxes andphospholipids were removed from the product. The fourth bar represents alighter color change as compared to the original product, and the fifthbar represents the removal of hexanol to eliminate the bad taste.

FIG. 4

FIG. 4 shows results for the percentage of oil removed for a variety ofcommercially available cooked food products. The bars represent thefollowing products, from left to right in the graph: (1) grilledhamburger meat, (2) cooked french fries, (3) wheat flour gravy mixhaving 51% hydrogenated soya oil, (4) potato chips, and (5) corn chips.Both the hamburger meat and french fries were obtained from a localMcDonald's® restaurant. When the soya oil was separated from the gravymix, the oil and flour carried an excellent taste from the originalproduct. As can be seen by the results, this process removed enough oilto allow "low fat" or "no fat" labeling of all these products.

FIG. 5

FIG. 5 shows results for the flavor, color, and shape (after oilextraction) for a variety of commercially available cooked food productscompared to a control group of hexane and CO₂ extracted cocoa powder(10%-12% butter fat). The bars represent the following products, fromleft to right in the graph: (1) grilled hamburger meat, (2) cookedfrench fries, (3) potato chips, (4) corn chips, and (5) cocoa powder.The test panels for flavor, color, and shape consisted of four differentgroups, where each group comprised three individuals.

Both the hamburger meat and french fries were obtained from a localMcDonald's® restaurant. The cocoa powder consisted of 10%-12% cocoabutter which was extracted to less than 0.05% cocoa butter, and wascompared for flavor, color and shape to hexane and CO₂ extracted cocoapowder having less than 0.5% cocoa butter.

FIG. 6

FIG. 6 shows extraction results over eight (8) tests for a number ofname brand cocoa powders as compared to a control level of 11% butterfat. The products were selected from Gerken's cocoa, Dutch cocoa fromHolland, and Savannah cocoa from Georgia. For each of these tests, theflavor, taste and color of the processed cocoa were far superior tohexane extracted cocoa butter. Ten test panels using blind taste testsconfirmed that the flavor of the cocoa processed according to theinvention exceeded the original control powder by over 50% of the testpanelists.

It should be noted that in Test No. 5, lumps were created in the reactorwhen nitrogen pulsing and pressure phase change control was eliminated.This lack of nitrogen pulsing allowed the solvent to bypass some of thematerial which changed phase and froze into oil-rich lumps of cocoapowder.

What is claimed is:
 1. A process for extracting oil from an oil-bearingcooked food product, which process comprises treating the cooked foodproduct with a normally gaseous solvent selected from the groupconsisting of butane, propane, and mixtures thereof, and separatingoil-laden solvent from said cooked food product of reduced oil content.2. The process of claim 1 wherein the extraction zone is maintained at atemperature from about 60° F. to about 130° F.
 3. The process of claim 2wherein the extraction zone is maintained at a temperature from about70° F. to about 110° F. and at pressures ranging from pressures lessthan atmospheric pressure to about 200 psig.
 4. The process of claim 3wherein the solvent molecules are stressed by fluctuating the pressureduring extraction by at least 0.25 psig.
 5. The process of claim 1wherein the oil-bearing cooked food product is a fried food based on afood selected from the group consisting of potatoes and corn.
 6. Theprocess of claim 3 wherein the fried food is selected from potato chipsand corn chips.
 7. The process of claim 1 wherein the oil-bearing cookedfood product is a meat based food product.
 8. The process of claim 7wherein the oil-bearing meat based food product is chopped beef.
 9. Aprocess for extracting oil from a food which has been cooked in oil,thereby resulting in an oil-bearing food product, which processcomprises:(a) placing said oil-bearing cooked food product into anextraction zone; (b) removing air from said extraction zone; (c)introducing a normally gaseous solvent selected from butane, propane,and mixtures thereof, into the extraction zone so as to contact saidoil-bearing cooked food product; (d) providing a pressure and atemperature in said extraction zone which is effective for maintainingthe solvent in a liquid phase; (e) maintaining the solvent in contactwith the oil-bearing cooked food product for an effective amount of timeto remove a predetermined amount of oil; (f) introducing an inert gasinto said extraction zone in a manner to displace said solvent andextracted oil from said extraction zone while maintaining temperaturesand pressures in said extraction zone which are effective formaintaining said solvent in a liquid phase; (g) passing said displacedextracted oil and solvent to a separation zone under conditions whichwill maintain the solvent in the liquid phase; (h) separating saidsolvent from said extracted oil in said separation zone; (i) collectingsaid extracted oil; and (j) collecting the cooked food productcontaining substantially less oil.
 10. The process of claim 9 whereinthe solvent is passed from the extraction zone to the separation zone byintroducing an inert gas into said extraction zone thereby displacingthe solvent at substantially the same temperature and pressure as thesolvent passes through the oil-bearing material and out of theextraction zone.
 11. The process of claim 10 wherein the extraction zoneis maintained at a temperature from about 70° F. to about 110° F. and atpressures ranging from pressures less than atmospheric pressure to about200 psig.
 12. The process of claim 11 wherein the oil-bearing foodproduct sits on a filtering screen which allows the passage of solventand oil, but not the material itself.
 13. The process of claim 12wherein the solvent molecules, during extraction, are stressed byfluctuating the pressure by at least about 0.25 psig.
 14. The process ofclaim 13 wherein the molecules of solvent are stressed by use ofsonication.
 15. The process of claim 9 wherein the cooked food productis a fried food based on a food selected from the group consisting ofpotatoes and corn.
 16. The process of claim 15 wherein the fried foodproduct is selected from potato chips and corn chips.
 17. The process ofclaim 9 wherein the oil-bearing cooked food product is a meat based foodproduct.
 18. The process of claim 17 wherein the oil-bearing meat basedfood product is chopped beef.
 19. The process of claim 13 wherein thecooked food product is a fried food product selected from those based ona food selected from the group consisting of meat, potatoes, and corn.20. The process of claim 19 wherein the cooked food product is selectedfrom potato chips and corn chips.